Cosmology with quasars: predictions for eROSITA from a quasar Hubble diagram

Understand

Our group has developed a technique that makes use of the observed non-linear relation between the ultraviolet and the X-ray luminosity in quasars to provide an independent measurement of their distances, thus turning quasars into standardizable candles.

• This technique, at present, it is mostly based upon quasar samples with data from public catalogues both in the X-rays and in the optical/ultraviolet and extends the Hubble diagram of supernovae to a redshift range still poorly explored (z>2).
• From the X-ray perspective, we are now on the eve of a major change, as the upcoming mission eROSITA is going to provide us with up to ~3 millions of active galactic nuclei across the entire sky.
• Here we present predictions for constraining cosmological parameters such as the amount of dark matter ($\Omega_{\rm m}$), dark energy ($\Omega_\Lambda$) and the evolution of the equation of state of dark energy ($w$) through the Hubble diagram of quasars, based on the 4-year eROSITA all-sky survey.